Hitherto, traffic calming humps (which are often colloquially referred to as xe2x80x9csleeping policemenxe2x80x9d) have conventionally comprised rigid structures laid across the road where calming is required. Typically, the humps are made, in situ, of tarmac and are integrated into the road surface. Alternatively, although less often, they comprise pre-fabricated structures made of, for example, steel which are secured to the road by suitable fasteners. In any event, these conventional humps have disadvantages. For example, they may present no less discomfort to occupants of a vehicle travelling at an acceptably low speed (say up to 30 mph) than to those of one travelling at an excessive speed. Also, they are potentially hazardous to vehicles such as ambulances and fire engines which, in the case of an emergency, might be travelling at a relatively high speed.
In order to overcome or mitigate those disadvantages, the use of xe2x80x9creactivexe2x80x9d traffic calming humps has been proposed. One type of reactive hump, with which the present invention is especially concerned, is disclosed in UK patent application GB-A-2324326 and corresponding PCT application No WO 98/40563 and comprises a pre-fabricated enclosure containing air and including a resiliently flexible, upper, hump-shaped membrane. It operates on the principle that when, on the one hand, the wheels of, for example, a car contact the membrane at a relatively low speed, the enclosure will progressively deflate under the weight of the car thereby causing little discomfort to the occupant(s). On the other hand, at excessive speeds, deflation is substantially prevented and the membrane maintains its hump-shaped form, thereby jolting the occupant(s) and inducing the driver to slow down prior to reaching the next hump. Further, the hump should preferably provide a relatively smooth passage for emergency vehicles, particularly ambulances, regardless of their speed of travel. The means hitherto proposed to control deflation of such type of reactive hump have not been entirely satisfactory. It is an object of the invention to provide valve means adapted especially, but not exclusively, for permitting or substantially preventing, as the case may be, deflation and collapse of a reactive traffic calming hump of the type described above.
According to a first aspect of the present invention, there is provided a reactive traffic calming device comprising a resiliently deformable enclosure containing air, air within the enclosure communicating with the atmosphere via a valve arrangement permitting the enclosure to be deflated under the weight of a passing vehicle and to re-inflate after passage of the vehicle, said valve arrangement comprising a pressure-sensitive valve adapted to remain open while the air within the enclosure is up to a first pressure threshold, thereby permitting deflation, and to close in response to pressure above said first pressure threshold, thereby preventing deflation in response to excessive vehicle speed.
The pressure-sensitive valve may comprise a first valve closure biased into a normally-open position and movable to a closed position, the air pressure within the enclosure impinging on said first valve closure to overcome said biasing means above said first pressure threshold.
The first valve closure may for example comprise a member having a shaft portion mounted to slide within a bore, and a broader, head portion responding directly to the air pressure. The biasing means may in this case comprise a coil spring surrounding the shaft portion and acting against the head portion.
The valve arrangement may further comprise means defining a sensing chamber surrounding the first valve closure, said inlet chamber communicating with the air within the enclosure via a restricted air inlet. This provision isolates the closure from transient air movements within the enclosure, promoting a more reliable response and avoiding spurious and intermittent actuation of the valve.
The restricted inlet may be arranged so as to direct air in a jet directly at the closure member. This feature may provide a more positive actuation of the valve.
The valve arrangement may further comprise a second valve, normally closed, arranged so as to open and allow rapid deflation of the device in response to pressure exceeding a second pressure threshold, greater than the first pressure threshold. This behaviour permits the desirable response to emergency vehicles, which are characterised by high weight and speed.
The second valve may comprise a second valve closure movable against second biasing means from a normally closed position to an open position.
The first and second valves may be integrated in a single unit. One such embodiment provides a fluid flow control valve comprising a body defining a fluid inlet and a fluid outlet, the body housing, intermediate the fluid inlet and the fluid outlet, first and second valves, the first valve including a first valve closure movable, against a first biasing means, from a normally-open position to a closed position and the second valve including a second valve closure movable, against a second biasing means, from a normally-closed position to an open position, the arrangement being such that, upon the application at the inlet of fluid pressure below a pre-determined lower value, the first and second valves maintain their normally open and closed positions respectively whereby fluid at the inlet can exhaust through the outlet via said first valve, that upon the application at the inlet of fluid pressure at or above said pre-determined lower value, but below a pre-determined higher value, the fluid pressure causes the first valve closure to move to its closed position while the second valve maintains its closed position whereby fluid is prevented from flowing through the control valve, and that, upon the application at the inlet of fluid pressure at or above said pre-determined higher value, the fluid pressure causes the first valve closure to move to its closed position and the second valve closure to move to its open position whereby fluid at the inlet can exhaust through the outlet via the second valve.
The embodiment described therefore provides a pressure sensitive valve that will respond in one or other of three different ways depending upon the increased fluid pressure applied to its inlet. In the context of a reactive road hump of the type described above, the valve functions as follows.
In a first case, when the wheels of a vehicle, such as a car, surmount the hump, the air in the enclosure will increase in pressure. Provided, however, that the vehicle is travelling at, or less than a pre-determined xe2x80x9csafexe2x80x9d speed, the pressure increase in the enclosure, and therefore at the inlet of the control valve, will be limited and insufficient to cause the first valve to close, as air will be able to exhaust from the enclosure via the first valve and the outlet of the control valve. The flexible membrane therefore progressively collapses and the vehicle""s occupant(s) will experience little or no discomfort.
In an alternative case, if the vehicle is travelling at a speed in excess of the pre-determined safe speed, the sudden pressure increase will be sufficient to cause the first valve to close, but will generally be insufficient to cause the second valve to open. Exhaust of air from the enclosure will therefore be substantially prevented and so the hump will more or less maintain its normal form and the occupant(s) will experience a discomforting jolt, thus inducing the driver to slow down.
Further, in the case of, for example, heavy emergency vehicles, the pressure increase will, more or less regardless of speed, be sufficiently high to cause the first valve to close and the second valve to open, whereupon air can exhaust from the enclosure and the flexible membrane will collapse and little or no discomfort will be experienced.
In a preferred, very compact, embodiment of a fluid flow control valve of the invention, the first valve closure comprises a generally annular member, the periphery of which co-operates with an annular seat of the first valve, and which defines a central passageway incorporating the second valve closure, the latter being operative to open or close the passageway as the case may be. Especially in that embodiment, the body is preferably generally cylindrical with the fluid inlet and fluid outlet being located at opposite ends thereof.
The biasing means may for example be compression springs, such as helical coil springs. Of course, other forms of spring may be suitable.
As will be appreciated, the reactivity of the hump may be varied as desired by varying the closing and opening characteristics of the first and second valves, as is described in more detail below. This may be by selection of the spring or other biasing means, by adjustments of geometry, or selection of parts of different geometry.
The invention further provides a valve arrangement for use in a reactive traffic calming device of the type described incorporating, first and optionally second fluid flow control valves adapted to operate as defined above. The valves may be arranged to be located separately in the wall but preferably they are integrated into a unitary body as defined by the first aspect of the invention.